1. Field of the Invention
The present invention relates to an addition-curable silicone resin composition, and relates specifically to a resin composition which, by combining different organopolysiloxanes having linear, branched and resin structures, yields a cured product that exhibits minimal tack. This composition is particularly useful as an inner encapsulant for a light emitting diode (hereafter abbreviated as “LED” unless otherwise noted).
2. Description of the Prior Art
Addition-curable silicone rubber compositions form cured products that are excellent in weather resistance, heat resistance, and rubber-like properties such as hardness and elongation, and are therefore used in a wide variety of applications, including as encapsulants for LED packages. However, because these cured products tend to suffer from surface tack, various problems can arise, including adhesion of dust to the cured product surface, and unintended bonding due to the tack between packages within the parts feeder used for sorting the final products.
A hard silicone resin may be used to prevent surface tack, but the resulting cured product tends to suffer from poor shock resistance, and tends to be particularly prone to cracking when exposed to thermal shock.
Accordingly, methods that utilize the properties of both an addition-curable silicone rubber composition and a hard silicone resin have been proposed, including a method in which the strength of the cured product is improved by adding a resin-like organopolysiloxane to an addition-curable silicone rubber composition, and a method in which a resin is coated onto the cured product of an addition-curable silicone rubber composition (see Patent Documents 1 and 2). However, in the former method, the degree of tack suppression is insufficient, whereas the latter method not only requires the formation of a two-layer structure, meaning the production process is more complex, but components within the upper layer resin also tend to seep into the lower layer, changing the cured product over time.
[Patent Document 1] US2007/0077360A1
[Patent Document 2] JP 2007-103494 A